The invention relates to mixer and burner assemblies, and more particularly to mixer and burner assemblies for forced draft combustion systems.
A conventional forced draft combustion system is disclosed in U.S. Pat. No. 5,171,144, which is assigned to the assignee hereof. A conventional system is also illustrated in FIG. 1. The system includes a cylindrical combustion chamber 1, a mixer and burner assembly 2 extending into the combustion chamber, a blower 3 for supplying air to the mixer and burner assembly, and a heat exchanger coil 4 surrounding the mixer and burner assembly in the combustion chamber. The mixer and burner assembly includes a mixing tube 5 having an open upper end, a closed lower end, and a cylindrical side wall 6 extending between the ends. The side wall is foraminous or porous, i.e., the side wall has therein many small orifices 7 through which combustion air flows out of the tube. The air is ignited by an ignitor 8 outside of the tube and heats liquid in the heat exchanger coil.
In order to evenly distribute air pressure over the length of the tube, the system also includes a pressure distribution cone 9 inside the tube. The pressure distribution cone is made of perforated metal, and the base of the cone sits on the closed lower end of the tube. Without the cone, air pressure tends to be significantly greater near the closed end of the tube than near the open end. This results in more flame adjacent the closed end. The cone equalizes air pressure over the length of the tube, so that the flame is substantially the same over the length of the tube.